Infection of covid-19 can be transmitted by asymptomatic infected people during speech, researchers have revealed, who recommend the use of a mask and visor in close situations such as going to a consultation or to the hairdresser.
Most studies focus on the flow of exhaled air through coughing or sneezing, which can send aerosols over long distances. However, talking close to each other is also a risk, since the virus can be transmitted through speech.
In a statement, the American Institute of Physics, concerning the study published in the Physics of Fluids scientific bulletin, Japanese scientists used smoke and laser light to investigate the flow of air expelled near and around two people, while talking in various common contexts, such as hairdressing salons, medical clinics or long-term care units.
In that investigation, electronic cigarettes were used to produce artificial smoke, containing droplets about a tenth in diameter, similar to the size of a virus particle.
The liquid used in these vaporization devices, a mixture of glycerin and propylene glycol, produces a cloud of tiny droplets that scatter light from a laser, allowing you to view airflow patterns. “We analyzed the characteristics of the diffusion of air exhalation with and without a mask when the person was standing, sitting, facedown or lying face up”, disse a autora Keiko Ishii.
To study the effect of speech on exhalation, the word “onegaishimasu”, a typical Japanese greeting in business settings, was pronounced repeatedly during the filming of the resulting vapor cloud.
The experiments were carried out in a hairdressing salon in Tokyo, with postures chosen to simulate typical customer service scenarios, including washing in which the customer is lying down and the technician standing and leaning over the customer.
“Similar face-to-face contacts would occur not only in that context, but also in medical and long-term care,” said Ishii.
The demonstrations revealed that the air exhaled by a person without a mask when speaking tends to move downwards under the influence of gravity, which is why if a client or a patient is lying down they can be infected.
When a mask is worn in a context where the person is standing or sitting, the cloud of vapor tends to stick to the person’s body, which is hotter than the air around them and moves upwards along from the body, which is why if the professional is bent, the aerosol tends to detach from the person’s body and fall on the client or patient.
The researchers also experimented with face shields and found that they can prevent the aerosols coming out of the mask from reaching the client or the patient.
That researcher concluded that “it is more effective to use a mask and face shield when providing services to clients”.